Been listing a collection of D&D and AD&D modules. There were a couple of green module A1s: Slave Pits of the Undercity. One of them was a 1st printing so I got a chance to compare to later printings. 1st prints aren’t super rare, but neither are they common.
1st print A1 modules have tiny printing artifacts that were fixed in subsequent printings.
Slave Pits of the Undercity (A1)
1980 … David Cook … 24 pages … TSR 9039 … ISBN 0935696253
Some of the interior illustrations have small circular blemishes on them (on pages 10, 12, and 14).
Later printings removed the artifacts.
Above is page 12 from both printings. 1st print top, 3rd print below.
I quickly discovered that the blemishes are faint, and don’t show up well in photos.
So I took some close-ups. Below is the full illustration from page 10 of the 1st print, and the close-up.
I’d say the blemishes are barely noticeable, except on Page 12. But I like the attention to detail in this case at TSR: They felt such trivial flaws worth correcting, so there’s that.